Antimissile efforts may use directed-beam weapons, in which the future missile or target location is not of particular interest, as the speed of the beam is so great that the missile motion is irrelevant. In those cases in which antimissile interceptors are used, the interceptor speed is of the same order as that of the target missile, and the estimated future location of the target missile is of great importance. A great deal of effort has been put into antimissile interceptor guidance schemes which predict the future location of the target missile, the interceptor missile, or both, so as to attempt to cause the interceptor to get within a given range of the target missile. These guidance systems require measurements of the target missile so as to determine its current location, and also require estimates of the type of missile, the stage of operation if it is multistage, and its projected trajectory.
It is known that rocket engine or rocket motor plumes are hot, and radiate energy across the entire electromagnetic spectrum. The radiated energy constitutes a signature allowing the rocket engine to be identified or characterized. Different missile systems using either liquid or solid propellant display different infrared (IR) signatures at various altitudes, mach numbers, and aspect angles. These IR signatures have been used for many years to warn of Intercontinental Ballistic Missile (ICBM) launches or to characterize tactical threat systems.
Radar systems have been used for tracking hostile missiles. In general, the radar returns were processed to determine the current location of the hostile missile, and to provide the location information to processors, such as Kalman processors, which attempted to predict the future location of the hostile missile.